JSP EL表达式使用：
Servlet:
package com.stono.servlet; import java.io.IOException; import java.util.HashMap; import java.util.Map; import javax.servlet.RequestDispatcher; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.stono.servlet.bean.Dog; import com.stono.servlet.bean.Person; import com.stono.servlet.bean.Toy; public class TestServlet6 extends HttpServlet { private static final long serialVersionUID = 1L; @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { Person person = new Person(); Dog dog = new Dog(); Toy toy = new Toy(); toy.setName("toyName"); dog.setName("dogName"); dog.setToy(toy); person.setDog(dog); person.setName("personName"); req.setAttribute("person", person); String[] musics = new String[] { "m1", "m2", "m3" }; req.setAttribute("musics", musics); Map<String, Object> map = new HashMap<String, Object>(); map.put("a", "ma"); map.put("b", "mb"); map.put("c", "mc"); req.setAttribute("map", map); Map<String, Object> map2 = new HashMap<String, Object>(); map2.put("a", "m2a"); req.setAttribute("map2", map2); req.setAttribute("aref", "a"); RequestDispatcher dispatcher = req.getRequestDispatcher("index016.jsp"); dispatcher.forward(req, resp); } }
JSP:
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> <% String path = request.getContextPath(); String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/"; pageContext.setAttribute("pca", "pageContextAttribute"); //session.setAttribute("s", "session"); %> <!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>016</title> </head> <body> <p>JSP生成的java文件中，EL表达式使用统一的方式进行数据读取；</p> <p>EL result is : ${pageScope.pca }</p> <p>person.name is : ${person.name }</p> <p>person.dog.name is : ${person.dog.name }</p> <p>musics[0] is : ${musics[0]}</p> <p>musics["1"] is : ${musics["1"]}</p> <p>musics["2"] is : ${musics[1+1]}</p> <p>map[a] is : ${map[a] }</p> <p>map["a"] is : ${map["a"] }</p> <p>map.a is : ${map.a }</p> <p>[]中没有引号，就会计算括号中的内容：</p> <p>map2[aref] is : ${map2[aref] }</p> <p>map2["aref"] is : ${map2["aref"] }</p> <p>person.dog.toy.name is : ${person.dog.toy.name}</p> <p>XXX is : ${XXX }</p> <p> ${pageScope } ${requestScope } ${sessionScope } ${applicationScope } ${param } ${paramValues } ${header } ${headerValues } ${cookie } ${initParam } ${pageContext } </p> </body> </html>
JSP转换生成的Java：
/* * Generated by the Jasper component of Apache Tomcat * Version: Apache Tomcat/7.0.35 * Generated at: 2015-10-30 00:31:49 UTC * Note: The last modified time of this file was set to * the last modified time of the source file after * generation to assist with modification tracking. */ package org.apache.jsp; import javax.servlet.*; import javax.servlet.http.*; import javax.servlet.jsp.*; import java.util.*; public final class index016_jsp extends org.apache.jasper.runtime.HttpJspBase implements org.apache.jasper.runtime.JspSourceDependent { private static final javax.servlet.jsp.JspFactory _jspxFactory = javax.servlet.jsp.JspFactory.getDefaultFactory(); private static java.util.Map<java.lang.String,java.lang.Long> _jspx_dependants; private javax.el.ExpressionFactory _el_expressionfactory; private org.apache.tomcat.InstanceManager _jsp_instancemanager; public java.util.Map<java.lang.String,java.lang.Long> getDependants() { return _jspx_dependants; } public void _jspInit() { _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory(); _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig()); } public void _jspDestroy() { } public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response) throws java.io.IOException, javax.servlet.ServletException { final javax.servlet.jsp.PageContext pageContext; javax.servlet.http.HttpSession session = null; final javax.servlet.ServletContext application; final javax.servlet.ServletConfig config; javax.servlet.jsp.JspWriter out = null; final java.lang.Object page = this; javax.servlet.jsp.JspWriter _jspx_out = null; javax.servlet.jsp.PageContext _jspx_page_context = null; try { response.setContentType("text/html;charset=UTF-8"); pageContext = _jspxFactory.getPageContext(this, request, response, null, true, 8192, true); _jspx_page_context = pageContext; application = pageContext.getServletContext(); config = pageContext.getServletConfig(); session = pageContext.getSession(); out = pageContext.getOut(); _jspx_out = out; out.write(' '); out.write(' '); String path = request.getContextPath(); String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/"; pageContext.setAttribute("pca", "pageContextAttribute"); //session.setAttribute("s", "session"); out.write(" "); out.write("<!DOCTYPE html> "); out.write("<html> "); out.write("<head> "); out.write("<meta charset="UTF-8"> "); out.write("<title>016</title> "); out.write("</head> "); out.write("<body> "); out.write(" <p>EL result is : "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${pageScope.pca }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write("</p> "); out.write(" <p>person.name is : "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${person.name }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write("</p> "); out.write(" <p>person.dog.name is : "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${person.dog.name }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write("</p> "); out.write(" <p>musics[0] is : "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${musics[0]}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write("</p> "); out.write(" <p>musics["1"] is : "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${musics["1"]}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write("</p> "); out.write(" <p>musics["2"] is : "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${musics[1+1]}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write("</p> "); out.write(" <p>map[a] is : "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${map[a] }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write("</p> "); out.write(" <p>map["a"] is : "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${map["a"] }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write("</p> "); out.write(" <p>map.a is : "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${map.a }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write("</p> "); out.write(" <p>[]中没有引号，就会计算括号中的内容：</p> "); out.write(" <p>map2[aref] is : "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${map2[aref] }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write("</p> "); out.write(" <p>map2["aref"] is : "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${map2["aref"] }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write("</p> "); out.write(" <p>person.dog.toy.name is : "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${person.dog.toy.name}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write("</p> "); out.write(" <p> "); out.write(" "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${pageScope }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write(" "); out.write(" "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${requestScope }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write(" "); out.write(" "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${sessionScope }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write(" "); out.write(" "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${applicationScope }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write(" "); out.write(" "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${param }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write(" "); out.write(" "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${paramValues }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write(" "); out.write(" "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${header }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write(" "); out.write(" "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${headerValues }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write(" "); out.write(" "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${cookie }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write(" "); out.write(" "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${initParam }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write(" "); out.write(" "); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${pageContext }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false)); out.write(" "); out.write(" </p> "); out.write("</body> "); out.write("</html> "); } catch (java.lang.Throwable t) { if (!(t instanceof javax.servlet.jsp.SkipPageException)){ out = _jspx_out; if (out != null && out.getBufferSize() != 0) try { out.clearBuffer(); } catch (java.io.IOException e) {} if (_jspx_page_context != null) _jspx_page_context.handlePageException(t); else throw new ServletException(t); } } finally { _jspxFactory.releasePageContext(_jspx_page_context); } } }